1. Field of the Invention
The invention relates to an aimable nozzle for injecting pulverized coal into the combustion chamber of a thermal power plant boiler, the nozzle including a first metal housing in the shape of a truncated prism having a top face, a bottom face and two lateral faces, a second metal housing in the shape of a truncated prism coaxially surrounding the first housing and defining therewith an annular space through which passes a flow of secondary air, and two pivots for rotation about an axis perpendicular to the lateral faces of the first housing, wherein the first housing channels a flow of primary air mixed with pulverized coal, the housings are fastened to each other and the interior of the first housing is divided by parallel refractory steel splitter plates perpendicular to the lateral faces of the first housing.
2. Description of the Prior Art
As is well known in the art, this type of nozzle is designed to be fitted to a pulverized coal burner mounted on the walls of a combustion chamber of a thermal power plant boiler, between an ashbox and heat exchangers.
It directs pulverized coal mixed with primary air into the combustion chamber. The nozzle is aimable so that it can be inclined in a vertical plane so that the air can be directed into an area of the combustion chamber at a greater or lesser distance from the screens, in order to adjust the heating power of the boiler.
Until now the first housing has been made in one piece by casting it in refractory steel, the second housing has been made from refractory steel plate bent to shape and welded and the splitter plates inside the first housing have been welded to its lateral faces. A nozzle of this kind is exposed to very high thermal stresses. In use, the temperature in front of the nozzle (at the face of the nozzle through which the primary and secondary airflows exit) can be as high as 900.degree. C. to 1000.degree. C., but the temperature is only 200.degree. C. to 300.degree. C. at the rear and the depth is only around 400 mm. Because of radiation phenomena inside the combustion chamber, areas in front of the nozzle can be exposed to high but different temperatures. It has been noticed that these high thermal stresses lead to deformation of the component parts of the nozzle, cracks in the cast components and ruptures of the weld between the splitter plates and the lateral faces of the first housing.
The object of the invention is to propose an aimable nozzle for injecting pulverized coal into the combustion chamber of a thermal power plant boiler which has improved resistance to these thermal stresses.
The basic idea of the invention is a nozzle consisting of welded or nested plates.